1. Field of the Invention
This invention relates to the use of tetrahydrocarbylphosphonium bicarbonate salts as catalysts for the preparation of epoxy-containing materials. More particularly, this invention pertains to a process for making a linear polymeric material from the advancement reaction of an epoxy resin with a polyhydric phenol (especially bisphenol A) in the presence of a tetrahydrocarbylphosphonium bicarbonate catalyst.
2. Description of the Prior Art
It is well-known in the art to produce hydroxyl-containing ethers by reacting a vicinal epoxide with a compound bearing phenolic hydroxyls in the presence of such catalysts as tertiary amines, quaternary ammonium halides, phosphonium halides and the like. See, for example: U.S. Pat. Nos. 2,216,099; 2,633,458; 2,658,855; 3,377,406; 3,477,990; 3,547,881; 3,547,885; 3,694,407; 3,738,862; 3,948,855; and 4,048,141. Canadian Pat. No. 893,191, German Pat. DT Nos. 2,206,218 and 2,335,199. The texts, Handbook of Epoxy Resins by H. Lee and K. Neville, McGraw-Hill (1967) and Epoxy Resins Chemistry and Technology, edited by C. A. May and Y. Tanaka, Marcel Dekker, Inc. (1973) are also of interest. It is taught in U.S. Pat. No. 4,048,141 that certain other phosphonium salts promote the reaction between vicinal epoxides and phenols and/or carboxylic acids or anhydrides.
U.S. Pat. No. 3,948,855, issued to Perry, teaches a process for preparing phenolic hydroxy ether compounds by the reaction of phenol and a vinyl epoxide in the presence of a phosphonium salt of an acid, ester or acid ester of the element carbon. However, a phosphonium bicarbonate salt is not disclosed in the formulae representing such phosphonium salts at column 6, lines 30-56, of the patent. Canadian Pat. No. 893,191, also issued to Perry, appears more relevant in that the formulae for the anion of the phosphonium salt disclosed at page 11, lines 1-9, include a bicarbonate anion amongst numerous other anions. However, nothing in this reference suggests that the phosphonium bicarbonate salt would be any more or less effective as a catalyst than the other phosphonium salts more explicitly described in this Canadian patent.
The prior art catalysts for promoting reactions of epoxides with phenols have generally been deficient in one or more aspects. In many instances, the PG,4 catalysts react with the epoxy reactant and thus preclude the marketing of a blend comprising an epoxy resin and a catalyst, a so-called "precatalyzed epoxy resin." Blends comprising a polyhydric phenol and a catalyst (i.e., a precatalyzed polyhydric phenol) have likewise been generally unavailable due to possible adverse reactions of the two components.
Many prior art catalysts exhibit a lack of selectivity in that they simultaneously promote the reaction of an epoxy resin with both the phenolic hydroxyl group(s) on the reactant and the aliphatic hydroxyl group(s) on the product, which produces branched or cross-linked polymers rather than the desired linear polymers. In still other instances, the molecular weight of the polymer attainable with the catalyst is limited. While a higher loading of catalyst will, up to a point, produce a polymer of a greater molecular weight than lower loadings, a limiting value for the loading is usually reached at which point little additional increase in molecular weight can be obtained by increasing the catalyst loading. These deficiencies have now been remedied by the subject invention.